import java.util.Arrays;

public class MyStack {
    private int[] elem;
    private int usedSize;
    private static final int DEFAULT_CAPACITY = 10;

    public MyStack() {
        this.elem = new int[DEFAULT_CAPACITY];
    }


    private boolean isFull(){
        return usedSize == elem.length;
    }
    //往栈中添加元素
    public void push(int val){
        if (isFull()){
            elem = Arrays.copyOf(elem,2*elem.length);
        }
        elem[usedSize] = val;
        this.usedSize++;
    }

    public boolean isEmpty(){
        return usedSize == 0;
    }
    public int pop(){
        if (isEmpty()){
            throw new no();
        }
        int oldVal = elem[usedSize-1];
        usedSize--;
        return oldVal;
    }
    public int peek(){
        if (isEmpty()){
            throw new no();
        }
        return elem[usedSize-1];
    }
}
